This invention related to a press apparatus for reducing widths of hot slabs by repeatedly pressing hot slabs in their width directions every feeding the slabs relatively to anvils, and a method of reducing the widths of the hot slabs by the use of the press apparatus.
It is very advantageous to change or reduce widths of slabs produced by continuous casting according to widths of plate products to be produced from the slabs before rolling in roughing mills. In this case, presses are effectively applied for the reduction in width, particularly, when widths to be reduced are large.
In reducing widths of slabs, it has been mainly used to combine "V-rolling" using vertical rolls and "H-rolling" using horizontal rolls. In order to prevent irregular shapes such as "fishtails" or "tongues" produced at preceding and trailing ends of slabs, a feature of preforming-pressing the preceding or trailing ends of slabs to prevent the irregular shapes has been disclosed in Japanese Laid-open Patent Application No. 58-53,301, wherein press apparatuses and vertical and horizontal rolling mills are provided to effect reversing rolling using vertical and horizontal rolls after pressing by the press apparatuses.
In order to carry out the width reducing method in existing hot rolling factories, strong vertical type reverse rolling mills, horizontal type reverse rolling mills and preforming presses for pressing preceding and trailing ends of slabs are needed. In fact, it is very difficult to obtain a wide space for locating these bulky apparatuses, and they increase initial cost of the installation.
In Japanese Laid-open Patent Application No. 59-101201, on the other hand, a continuous width reducing method with a press for slabs has been disclosed which is able to save a space and to decrease the initial cost of the installation. In this method, however, distances to be reduced in width of slabs should be set according to required reduced widths of slabs when initial widths of the slabs or widths of plate products are within various ranges. Such a setting of widths may detrimentally affect the efficiency in working for the continuous width reduction.
In reducing widths of slabs, moreover, buckling often occurs in the slabs. FIG. 1 illustrates relations between patterns of pressing slabs and shapes of buckling in the slabs. When a preceding end has been preformed, a large buckling would occur in the preceding end of the slab as shown in FIG. 1(a). When a trailing end has been preformed, a large buckling also occurs in the trailing end of the slab as shown in FIG. 1(c). In both the cases, the large bucklings occur at the free ends. In steady pressing that intermediate portions of slabs are pressed without preforming as shown in FIG. 1(b), a buckling is smaller than in the both cases of FIGS. 1(a) and 1(c). However, the buckling continues in the longitudinal direction to form one half of a pipe longitudinally split. In case of that steady pressing is continued to a trailing end without preforming the trailing end, the buckling becomes larger as the pressing becomes near to the trailing end so that the reduction in width to the trailing end is often impossible as shown in FIG. 1(d). When such bucklings are small, the inherently aimed change in width of slabs is impossible because the reduction in width of slabs is small. On the other hand, when such bucklings are large, it becomes difficult to cause the slabs to pass through rolling mills in addition to the impossibility of the change in width. Accordingly, it is absolutely necessary to prevent the buckling.
In the width reduction by vertical and horizontal roll rolling mills hitherto used, there is a possibility of buckling in rolling with the vertical rolling mills. Accordingly, the maximum value .DELTA.w of width reduction is usually set to be .DELTA.W&lt;1/2T.sub.0, where T.sub.0 is the initial thickness of the slab, so that the width reduction is effected within a range less than the limit value for preventing the buckling. With a sizing mill capable of controlling tensile forces between the vertical and horizontal roll rolling mills, tensile force is applied by the horizontal rolling mill on an exit side to a slab being rolled by the vertical rolling mill so as to increase the limit value to make large the reduction in width of the slab. However, this method also remains in the fact that the reduction in width is limited by the above limit value for preventing the buckling.
In contrast herewith, it has been also proposed to positively hold a slab by a set of holding rolls arranged at a center of width of the slab on an axis connecting vertical rolls of an edger in order to avoid the buckling (Japanese Laid-open Pat. Application No. 57-168707). Moreover, the feature of providing two sets of holding rolls on both sides of a center of width of the slab is disclosed in a text of lecture meeting "Iron and steel" published by Japanese Iron and Steel Society, autumn of 1983, 69-5 (1983) S350, 349. These methods make possible the reduction in width of slabs beyond above limit value.
In reducing width of hot slabs by means of a press using anvils having flat portions in parallel to proceeding direction of the slabs and inclined portions at their front and rear ends, on the other hand, there are three patterns of pressing, i.e., preforming preceding ends, preforming trailing ends and steady pressing, and deformed zones of the slabs are large. As a result, the buckling is likely to occur when the reduction in width is large. It has been found that only one holding position by holding means between anvils is insufficient.